The present invention relates to electrical polymer insulators with exterior semiconductive elastomeric corona protection devices. A corona protection device is attached or bonded to the insulator and is used to protect the insulator from polymer housing deterioration and to eliminate television and radio interference because of noise created by corona.
Electrical polymer insulators are used in power transmission and distribution systems to provide mechanical support for the conductors and provide electrical insulation between the high voltage conductors and grounded tower structures. A corona protection device is located at the line end and/or the ground end of the insulator and eliminates the corona discharge from the insulator. Elimination of the corona discharge protects the surface of the insulator from polymeric material deterioration caused by electric stress. In addition, eliminating the corona discharge reduces television and/or radio noise created by the corona discharge.
Present day corona protection devices are generally made of a metal, such as aluminum. These metal corona protection devices have a tendency to be mishandled during shipping and/or installation. Mishandling, such as dropping or striking the protection device against another object, causes mechanical damage to the corona protection device due to the rigid nature of the metal. This damage alters the shape of the corona protection device, which can result in a reduction in the protection device""s ability to eliminate a corona discharge.
In order for a corona protection device to operate properly, it must be in its original configuration. When the corona protection device is damaged due to mishandling the corona discharge may not be eliminated and polymeric material deterioration and radio and television noise are likely.
Examples for prior electrical insulators are U.S. Pat. Nos.: 3,192,312 to Sauer; 3,735,019 to Hess et al; 3,836,705 to Rosenblatt; 3,941,918 to Nigol et al; 4,103,103 to Hizikata; 4,343,966 to Pargamin; 4,443,659 to Tatem; 4,724,284 to Wheeler.
A need thus exists to overcome the inherent problems of the existing prior art, while maintaining the desired result of eliminating a corona discharge on an electrical insulator device.
Accordingly, an object of the present invention is to provide an electrical polymer insulator, particularly for power transmission and distribution systems, with a corona protection device that reduces polymeric material deterioration on the surface of the polymer insulator by eliminating the corona discharge.
Another object of the present invention is to provide an electrical polymer insulator with a corona protection device that will reduce television and radio interference or noise by eliminating the corona discharge.
A further object of the present invention is to provide an electrical polymer insulator with a corona protection device that is made of semiconductive elastomeric material, which would reduce or prevent possible damage to the device due to mishandling, thus saving possible maintenance time.
Yet another object of the present invention is to provide an electrical polymer insulator with a corona protection device that is made of semiconductive elastomeric material that eliminates costly metal materials for metal corona rings, which may reduce the cost of the device and insulator.
Yet another object of this invention is to provide an electrical polymer insulator with a corona protection device made of a semiconductive elastomeric compound that is resistant to weather, ultra-violet radiation, and electrical surface discharges.
Still another object of this invention is to provide a corona protection device that may vary in thickness and diameter, allowing a reduction in cost in the manufacturing of the protection device and also allowing a reduction in size, while still eliminating the corona discharge.
The foregoing objects are basically obtained by providing a polymer insulator with a fiberglass reinforced core and metal fittings at both ends of the core. A polymer weathershed housing surrounds the core with each end of the weathershed housing abutting one of the metal fittings. The weathershed housing is sealed to the end fittings through the use of metal shielding collars that overlap the end of both the weathershed housing and the metal fittings. A semiconductive elastomeric corona protection device is molded and bonded to the exterior of the polymer insulator end fittings.
The protection device may be molded to the metal fittings, the shielded collars or a portion of both the metal fittings and the shielding collars. The semiconductive rubber corona protection device eliminates the corona discharge emitted from the polymer insulator end fittings and is not likely to be damaged when it is shipped or installed due to the resilient nature of the elastomeric material.
Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which when taken in conjunction with the annexed drawings, discloses a preferred embodiment of the invention.